1. Field of the Invention
The present invention relates to an apparatus for converting free-flowing feed material into granules, agglomerates, pellets, compacts, and the like, as well as a shape component inside such an apparatus.
2. Description of the Background Art
It is generally known to convert, by compressing and heating, inorganic matter, which most often is thermoplastic synthetic material, frequently waste material to be recycled, into free-flowing granules, which are then used as a source material to be fed to extruders, injection molding machines, blowing machines, and the like. In the course of the forced mixing and compression of the feed material, friction heat is generated as a result of the inner friction associated therewith, which leads to a softening of the thermoplastic material. If the feed material is heated to or beyond a melting point of the respective material, plasticization occurs, which makes it possible for agglomerates to form. Additives like saw dust and wood fibers, for example, can be mixed into the synthetic materials. The plasticized synthetic material then assumes the function of a binding agent for the additive, binding its particles. If, on the other hand, the temperatures remain below the material-specific melting point, the feed material is merely heavily compressed, and compacts are generated, in the form of pellets, for example.
Organic feedstock or a blend of organic and inorganic materials can also be processed in a similar fashion. In addition to the previously mentioned wood particles, paprika powder, sugar, sugarcane fiber, starch, and the like are also suitable.
The challenge with these methods, and in particular with the agglomeration, is to control the temperature development in a suitable device such that on the one hand, there is sufficient heat available to convert the thermoplastic synthetic particles into the plasticized condition, but on the other hand, to avoid temperatures that are too high, because they could otherwise result in thermal damage to the material. The exact and constant maintenance of the correct material-specific temperature is thus a pre-requisite for a high-quality end product.
A known apparatus for this purpose is described in DE 32 10 974 A1, wherein shredded plastic film, after being shredded and cleaned, is converted into granules. Essentially, the apparatus is comprised of a conical extruder, which terminates in a crack or narrow annular chamber. The feed material is thereby continuously compacted in the pressing screw, thereby squeezing out the cleaning water before it reaches its highest density in the crack or the annular chamber. Due to the existing pressure and friction forces amongst the particles, enough heat is generated to dry out the feed material completely while forming compacts. By increasing the pressure against a perforated plate arranged at the upper face end of the crack or the annular chamber, thus increasing the temperature to the melting point of the feed material, a sintering process is started, which results in agglomerates.
A noticeable disadvantage thereof is that it is very difficult to achieve the course of action of the apparatus within the necessarily narrow temperature range. Due to the fact that the input material is already subjected to considerable pressure and shear forces in the extruder, the feed material heats up at a very early stage inside the apparatus. As a result of heat accumulation during the passage through the apparatus, the maximum temperature is thus reached long before the passage through the perforated plate so that cooling measures are necessary. The great temperature fluctuations associated therewith result in granules of non-uniform physical and chemical consistency, which limits their subsequent processing.
In contrast thereto, DE 38 42 072 C1, which corresponds to U.S. Pat. No. 5,009,586 and is assigned to the assignee of the present invention, discloses an apparatus that is much improved and well-proven in the field. The agglomerator described therein is comprised of a screw conveyor with material infeed, which conveys the feed material axially into a disk-shaped annular compression chamber. At its periphery, the compression chamber is confined by a perforated die, through which the feed material is pressed by a rotating pressing blade after sufficient compacting and heating.
Due to the crescent shape of the pressing blade and in conjunction with the perforated die, a compression zone that is tapered toward the perforated die is formed, into which the plastic particles are drawn in the course of the rotation of the pressing blade and are subsequently subjected to increasing pressure forces. At the same time, the forced mixing of the feed material due to the rotating pressing blade generates substantial shear and friction forces, which altogether causes a quick self-heating in the compression chamber.
Simultaneously with the temperature increase, a softening of the plastic particles occurs, which in turn lowers their adhesive resistance when passing through the perforated die. Therefore, a further increase of the pressure and shear forces is no longer possible when this condition is reached, because due to the associated increase in temperature, the feed material counteracts these tendencies by reducing the viscosity. Thus, a balanced condition is created, the parameters of which, like pressure, temperature and viscosity, essentially depend on the kind of feed material and the geometrical configuration of the compression zone.
Due to the described construction design of known devices, a manipulation of the parameters listed above to adjust defined materials or to attain defined characteristics of the end product is not possible, although this would be desirable in view of a broadest-possible field of application for the devices.